The present invention relates to an electricity-to-sound transducer such as a slender speaker having high sound quality.
With increased popularization of high-vision and wide-vision etc., TV sets with wide screens have widely been used. There is, however, increased demands in Japan for thin and not-so-wide TV sets and also audio component systems due to relatively poor Japanese housing conditions.
Speaker units for TV sets are for example one of the causes for TV sets that inevitably become wide. Because speaker units are mostly set on both sides of a cathode ray tube. Thus, most known speaker units have been not so wide such as rectangular and oval types. However, as cathode ray tubes become wide, there is a strong demand for slender speaker units as narrow as possible and for high sound quality that matches high picture quality in high-vision and wide-vision.
Known slender-type speakers, however, cannot meet such a demand due to distributed vibration that easily occurs in the long axis direction because of one-point driving at the center section of a slender diaphragm. This results in a peak dip in reproduced acoustic-pressure frequency characteristics in middle and high tone ranges, thus decreasing sound quality.
The applicant for this patent application has proposed, in Japanese Patent Application No. 10-192048, an electricity-to-sound transducer with flat frequency characteristics for high sound quality with less distributed vibration even though it is made as a slender structure.
This electricity-to-sound transducer is described with reference to FIGS. 5 to 8.
A reinforcing member 40 is inserted from above into each slot 38 formed at an almost center section of a diaphragm 31 in the longitudinal direction and almost perpendicular to this longitudinal direction. The diaphragm 31 is supported by the reinforcing member 40. Several materials can be used as the member 40 for supporting the diaphragm 31, such as metal, resin and wood. The member 40 is formed in a long rod with cuts 41 provided on the bottom surface at a constant interval. A voice coil 33 is passed through each cut 41 and wound around each of main vibrating portions 31a at the base section.
A magnetic field is generated around the voice coil 33 by magnets 35 to cause a drive current flowing the coil 33 for generating an electromagnetic force. The main vibrating portions 31a are vibrated by the electromagnetic force, and thus the diaphragm 31 is vibrated. During this vibration, however, distributed vibration is prevented from occurrence at the center section of the diaphragm 31 in the longitudinal direction because the slots 38 on the center section are supported by the reinforcing member 40.
Formed on the upper surface of each main vibrating portion 31a are convex semi-circular cylinder portions 39a and concave semi-circular cylinder portions 39b provided alternately in the longitudinal direction. This structure has a high mechanical strength (rigidity) against force to be applied in a direction perpendicular to the longitudinal direction. Without this structure, it could happen that a main vibrating portion 31a starts to vibrate larger or smaller than the neighboring one with no vibration in synchronism with each other at the border between the two vibrating portions. Such large and small vibration components are, however, complimentarily prevented from occurrence by employing the structure explained above.
FIG. 9 illustrates vibration occurring on the diaphragm 31 of the electricity-to-sound transducer described above in a free-vibration mode. Observed around the slots 38 is distributed vibration restricted in the free-vibration mode. Also restricted is distributed vibration occurring around the center section of the diaphragm 31 in the longitudinal direction.
FIG. 10 illustrates a result of numerical analysis on the frequency response characteristics of vibration amplitude around the center section of the diaphragm 31. The solid line xe2x80x9cAxe2x80x9d indicates the result on the electricity-to-sound transducer disclosed in Japanese Patent Application No. 10-192048. The dot line xe2x80x9cBxe2x80x9d indicates the result on another known electricity-to-sound transducer. Observed in this figure is that the known transducer suffers from amplitude depression at frequencies of about 13.5 KHz or more whereas, for the transducer in the Patent Application above, the frequency characteristics is improved such that peaks are depressed at a high frequency range around 10 KHz while depression at frequencies of about 13. 5 KHz or more is not so badly and this continues to 15 KHz.
These electricity-to-sound transducers, however, have drawbacks as discussed below with reference to FIGS. 11 and 12.
The diaphragm 31 is protected from distributed vibration at its center section in the longitudinal direction by means of the reinforcing member 40 inserted in the slots 38 from above, as indicated by arrows in FIG. 11, in the direction perpendicular to the longitudinal direction.
Considerably deep slots must be formed as the slots 38 for depth H shown in FIG. 11 for stably sustaining the reinforcing member 40. Such a deep slot, however, causes a problem in that an upper edge 34a of a voice coil bobbin 34 touches a lower edge 38a of each slot 38 when the bobbin wound a voice coil 33 is inserted from the bottom of the diaphragm 31, so that the bobbin cannot be fit in the prescribed position.
On the other hand, a slot 38 formed as not so deep for resolving such a problem on the voice coil bobbin 34 cannot resolve the problem in that the diaphragm is fallen inwardly at the center section as discussed above.
A purpose of the present invention is to provide an electricity-to-sound transducer that has a new structure for a diaphragm and a voice coil bobbin attached to the diaphragm with less abnormal vibration which may otherwise occur in the longitudinal direction due to natural frequency of the diaphragm, for normal sound irradiation in response to a large input.
The present invention provides an electricity-to-sound transducer comprising: a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm; an edge portion formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to the outer periphery, the edge portion sustaining the diaphragm for vibration; a voice coil bobbin having a winding portion around which a voice coil is wound split into two portions in the longitudinal direction of the diaphragm, the bobbin being attached to a rear surface of the diaphragm while the two portions are joined to each other, the joined portions forming a reinforcing beam that reaches a rear surface of a bottom of the slot of the diaphragm; a magnetic circuit for applying flux to the voice coil for vibration; and a frame for sustaining the outer periphery of the edge portion.
Moreover, the present invention provides an electricity-to-sound transducer comprising: a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm, the slot having walls on a bottom of slot, on both ends of the slot in a direction of the major axis and on both ends of the slot in a direction of the minor axis, the slot protruding in a direction of a rear surface of the diaphragm to form a protrusion; an edge portion formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to the outer periphery, the edge portion sustaining the diaphragm for vibration; a voice coil bobbin attached to the rear surface of the diaphragm, an inner size of the bobbin almost at the center in the longitudinal direction being larger than an outer size of the protrusion in the direction of the minor axis, the protrusion being inserted into the bobbin, a gap between an inner wall of the bobbin and the protrusion being filled with an adhesive so that the protrusion and the bobbin are bonded to each other; a voice coil wound around the voice coil bobbin; a magnetic circuit for applying flux to the voice coil for vibration; and a frame for sustaining the outer periphery of the edge portion.